The specific aims of our current research reflect our continued interest in understanding how the doublesex branch of the Drosophila sex determination hierarchy functions to direct growth, morphogenesis, and differentiation. We also want to understand how information from the sex determination hierarchy is integrated with information from developmental hierarchies specifying other aspects of development (e.g. segment identity, tissue and cell type, etc.) to govern development and differentiation. We are addressing the following topics: I. How is genital imaginal disc development controlled? Specific topics include: A. How is patterning of the mature third instar genital disc achieved? We are focusing on a newly discovered requirement for Abd-A function in the genital disc. B. What are the roles of genes that are sex-specifically expressed in the genital disc and how are the spatial and sexual patterns of expression determined? We are currently focusing on the roles of branchless (which encodes FGF), breathless (which encodes an FGF receptor), the pan-neural gene deadpan, bric-a-brac (which encodes a transcription factor), and sprouty (which encodes an antagonist of branchless), all of which we have shown to be sex-specifically expressed in the genital disc. II. We have used DNA microarrays to identify and characterize genes expressed sex-specifically in somatic cells. Our initial experiments identified 65 new genes that are sex-differentially expressed in somatic cells of adults and under control of the sex determination hierarchy. These genes are being characterized the roles of these genes in adult physiology and development. Additional microarray experiments are underway to identify genes expressed sex-differentially in somatic cells under the control of doublesex during earlier stages of development. II1. How do the compensasomes, the RNNproteins complexes that mediate dosage compensation, get to their final locations along the X chromosome, and how are the locations and extents of the bands they form delimited? IV. How has the process of sex determination evolved?